(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of precise temperature control in RTP low temperature operation and monitoring in the fabrication of integrated circuits.
(2) Description of the Prior Art
Rapid thermal processing (RTP) has been implemented in many thermal fabrication steps in integrated circuit manufacturing. Precise control of time and temperature are necessary for reproducible results in RTP processes. It is especially difficult to control rapid thermal annealing (RTA) systems and to match temperatures between systems in the low temperature region of between about 200 and 800xc2x0 C. Commonly, a pyrometer sensor is used for RTP temperature control. The sensor detects the actual wafer temperature by an emitted optical signal from the wafer. This optical signal is relatively low compared to a high temperature emission. The signal from the wafer:
Ixcex1xcex5T4
where T is the wafer temperature. For a lower temperature, the signal emitted from the wafer is smaller. If a thermocouple is used to detect the temperature, a lower temperature also results in a lower voltage signal from the thermocouple.
In the wafer fab or between fabs, the same or different hardware systems are used for RTP with the same recipe temperature settings for the same process. With current calibration systems, the absolute temperatures for the same recipe temperature setting can be different for each hardware system. This difference must be minimized in order to have system matching.
Temperature sensitivity curves, showing resistance versus temperature, have been used for system setup. However, wafer conditions and substrate composition have major impacts on the output sheet resistance of the RTP process. These factors are not included in temperature sensitivity curves. It is desired to find a method of more precise temperature control and temperature matching between systems.
U.S. Pat. No. 6,132,081 to Han discloses a method for determining a temperature for RTP to form titanium silicide. The temperature is set to be that temperature after which sheet resistance and/or nonuniformity are constant; that is, not sensitive to temperature. This method is also used to calibrate an optical sensor. This method will not be able to catch a temperature drift to the higher side and cannot be used in day-to-day system matching. U.S. Pat. No. 6,136,613 to Lin et al teaches a method of recycling monitoring control wafers including annealing and measuring sheet resistance. U.S. Pat. No. 5,331,676 to Lambert et al show a method of calibrating furnace temperature using a temperature probe. U.S. Pat. No. 5,326,170 to Moslehi et al shows calibration wafers having melting points of certain elements as calibration temperature points.
A principal object of the present invention is to provide an effective and very manufacturable method of temperature control in a rapid thermal process (RTP) system.
A further object of the invention is to provide a method of controlling RTP low temperature operation.
Yet another object is to provide a method of calibrating an RTP low temperature operation.
Yet another object is to provide a method of controlling and/or calibrating RTP low temperature operation by observing sheet resistance uniformity peak and uniformity change.
A further object is to provide a method of matching temperatures between RTP systems by detecting temperature shifts by observing sheet resistance uniformity peak and uniformity change.
A still further object of the invention is to provide a method of controlling and/or calibrating RTP low temperature operation by detecting temperature shifts by observing sheet resistance uniformity peak and uniformity change.
Yet another object is to provide a method of monitoring temperatures in a thermal processing system.
In accordance with the objects of the invention a novel method for calibrating RTP low temperature operations is achieved. A wafer comprising a silicon semiconductor substrate having a refractory metal layer thereon is silicided in a RTP system. Peak sheet resistance uniformity of the wafer is measured thereby detecting silicidation phase transition temperature points. Peak sheet resistance uniformity shifting from one temperature to another temperature indicates process shift. The temperature shift is used to reset and/or control the RTP system.
Also in accordance with the objects of the invention a novel method for controlling RTP low temperature operations is achieved. A wafer comprising a silicon semiconductor substrate having a refractory metal layer thereon is silicided in a RTP system. Peak sheet resistance uniformity of the wafer is measured thereby detecting silicidation phase transition first temperature points. Thereafter, a second wafer comprising a silicon semiconductor substrate having a different refractory metal layer thereon is silicided in the RTP system. Peak sheet resistance uniformity of the second wafer is measured thereby detecting silicidation phase transition second temperature points. The first and second temperature points are used for temperature calibration.
Also in accordance with the objects of the invention a novel method for matching temperatures of a plurality of RTP systems is achieved. A plurality of wafers comprising a silicon semiconductor substrate having a refractory metal layer thereon are silicided in each of a plurality of rapid thermal process systems. Peak sheet resistance uniformity of each of the wafers is measured thereby detecting silicidation phase transition temperature points for each of RTP systems. The temperature points having the highest uniformity are used to match temperatures for each of the RTP systems.
Also in accordance with the objects of the invention a novel method for controlling RTP system low temperature is achieved. A plurality of wafers comprising a silicon semiconductor substrate having different kinds of refractory metal layers thereon are silicided in a rapid thermal process system. The temperature can be as low as 200xc2x0 C. Peak sheet resistance uniformity of each of the wafers is measured thereby detecting silicidation phase transition temperature points for each of the types of wafers. These temperature points are used to control the RTP system.